Apparatus and method for test and debug of a processor/core having advanced power management

ABSTRACT

An interface unit is provided in a JTAG test and debug procedure involving a plurality of processor cores. The interface unit includes a TAP unit. A switch unit is coupled to the interface unit and switch units are coupled to each of the plurality of processor/cores. When the processor/cores have advanced power management systems, a sleep inhibit signal can be applied to the processor/core state machine preventing the state machine from entering a lower power state. The parameters of the processor/core can be tested to determine when the test and debug procedures can be implemented. When the (power) parameters are to low to permit test and debug, the test and debug unit can provide a command forcing the state machine into a state for which test and debug procedures can be implemented.

This application is a divisional of co-pending U.S. application Ser. No.11/411,381, filed on Apr. 26, 2006, which claims the priority under 35USC 119(e)(1) of U.S. Provisional Application No. 60/675,274(TI-36934PS), filed on Apr. 27, 2005. Both of the aforementionedapplications are incorporated herein by reference.

RELATED APPLICATIONS

U.S. application Ser. No. 11/411,670 (Attorney docket no. TI-36934),entitled APPARATUS AND METHOD FOR COUPLING A PLURALITY OF TEST ACCESSPORTS TO EXTERNAL TEST AND DEBUG FACILITY, and U.S. application Ser. No.11/411,683 (Attorney docket no. TI-62360), entitled APPARATUS AND METHODFOR CONTROLLING POWER, CLOCK, AND RESET DURING TEST AND DEBUG PROCEDURESFOR A PLURALITY OF PROCESSOR/CORES, both filed on Apr. 26, 2006, containsubject matter related to the subject matter of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the test and debug of multipleprocessors on a chip and, more particularly to the coupling of the testaccess ports (TAPs) associated with each processor to an external testand debug unit. The invention is specifically directed toward the testand debug of processor/cores having advanced power management.

2. Background of the Invention

Today's digital signal processors, microprocessor, and complex logiccores facilitate test via a limited pin interface called the JTAGinterface. This interface conforms to the IEEE 1149.1 Test Access Port(TAP) protocol and requirements. Modern processor units often use theJTAG interface to provide access to in-circuit emulation (ICE) logic inorder to facilitate debug of an embedded processor or logicsystem-on-a-chip designs. The processor unit often has multipleprocessors/cores, each processor/core having its own TAP.

The IEEE1149.1 specification has two ways in which multiple TAPs can beconnected together. In the parallel configuration, a single TDI (testdata in) input signal is connected to the TDI input of each TAP in thesystem. Similarly, the TDO (test data out) output signals from all ofthe processors/cores are wired together. A separate TMS control signalfor each TAP is used to drive each TAP state independently. Thecontroller assures that only one TAP at a time is put into a state inwhich it responds to the TDI input signals and transmits the TDO outputsignals.

The problem with a parallel configuration is that each TAP requires itsown TMS control signal. On a system-on-a-chip with multipleprocessor/cores, this configuration would require several pins on thedevice. In addition, each of these pins would need to be coupled to aJTAG controller. This coupling would require additional signals on theprocessor unit board and the connector to the JTAG controller. Thissolution to the problem of multiple TAPS is not conveniently scalable.Since only one TAP can drive its TDO output at the same time, theparallel solution also does not facilitate co-emulation in whichmultiple TAPs need to be driven through the TAP state machine at thesame time.

With the parallel configuration, one or more TAPs can be turned off orun-powered while preserving the ability to performs scans to activeTAPs. However, once a TAP becomes inactive, there is no way for acontroller to wakeup the module and re-enable scans.

The series configuration is the more common configuration for connectingmultiple TAPS. This configuration requires that all TAPs be clocked withthe same clock and the serial output of one TAP is used as the serialinput to the next TAP in the system. This configuration supports bothdebug and test procedures.

There are several problems with the series test configuration. First, ifthe power is removed from one TAP in the series, then the controllerwill be unable to shift data into and out of any TAP linked in serieswith the un-powered TAP. Once a TAP has been un-powered, the scancontroller is not able to wakeup the sleeping module. The second problemis that all TAPs must be clocked at the same frequency. Consequently,the maximum clock frequency is limited by the slowest component in thesystem. Synthesizable ARM processors from ARM Ltd exacerbate thisproblem since the JTAG TCK (test clock) clock signal must besynchronized with the ARM processor functional clock. This synchronizedTCK signal, called the RTCK signal, must be used as the TCK signal forall other components linked in series with the ARM processor. Therefore,if the ARM clock is running at a slow frequency or is turned off,scanning through any of the TAPs in series with this core is notpossible.

Another problem with the series configuration of TAPs is that to accessone particular TAP, the controller must scan through all of the TAPs inthe series. This feature makes scaling difficult. Systems or evensystems-on-a-chip may have hundreds of processors. This complexity leadsto a scan path that is thousands of bits long. A long scan pathsignificantly slows debug of a selected processor core.

The series configuration also presents problems for production testing.Typically, the test vectors used in a production test are written for asingle TAP. The test harness does not have an automated method tounderstand that other TAPs may precede or follow the TAP under test inthe JTAG series. For each system, these test vectors must be rewrittento accommodate several TAPs in series.

In order to protect confidential information being processed on anembedded device, some devices are equipped with security features toblock viewing of some data. Security features on a system may also beused to protect intellectual property, such as algorithms, drivers, orother software. Because debug procedures use the TAP on a processor toaccess ICE logic, security logic often disables the TAP on the protectedcore. In past designs, the TAP was disabled by gating the TCLK signal,which is the TAP clock signal.

Gating the TCLK signals presents several problems. First, gating theTCLK signal at the device level blocks debug and test procedures accessto all TAPs and hence all processor/cores to in the system. Thisunsophisticated technique does not allow for visibility in the protectedsystem while blocking visibility into other systems. Even if the TCLKsignal was gated closer to the processor/core's TAP, this implementationwould not help because the TAPs are connected in series. For theshifting through the series TAPs to be implemented, the TCLK signal mustbe enabled to all TAPs in the chain. The second problem is that blockingvisibility into the system is in direct conflict with the needs of debugprocedures that seek to give full visibility into the system. A methodis needed to selectively and dynamically enable or disable access to allTAPs in a system.

Referring to FIG. 1, the configuration for testing a plurality ofprocessor/cores 11-1N fabricated on a circuit board 1 according to theprior art is shown. Processor/cores 11-1N each includes a Test AccessPort (TAP) unit 111-11N, respectively. A host processing unit 3, theapparatus that controls the testing of the processor/cores 11-1N,exchanges signals with an emulation unit 2. The emulation unit 2 formatsthe signals received from the host processing unit and applies theresulting signals to TAP units 11-1N. Each TAP unit 11-1N receives theTMS signal, the TCLK signal and the TRST signal. With respect to the TDIand TDO signals, the TAP units are coupled in series, the TDI signalbeing applied to the first TAP unit 11 in the series and the TDO signalbeing received from the last TAP unit 1N in the series.

Referring to FIG. 2, a block diagram of a TAP unit 20 according to theprior art is shown. The TAP unit 20 includes a state machine 21. Thestate machine, in response to the TMS signal, the TRST signal, and theTCLK signal generates control signals that control the sequencing andactivity of the TAP unit 21. The TDI signal is applied to the switchunit 23. Switch 23 directs the TDI signals to the IR register 25 or toone of the DR registers 26-2N. The output signals of the registers areapplied to the multiplexer 24, the output of the multiplexer 24 beingthe TDO signal. When the TDI is applied to the IR register 25, thecontents of the IR register are applied to a logic unit 22. The logicunit 22 provides control signals that specify a test and debug activity.

The operation of the TAP unit 20 can be summarized as possible. A valueis entered in the IR register 25. In response to the value, an activityis implemented by control signals generated by the logic unit 22. Thisresult of a value in the IR register can be a transfer of a value fromthe DR register to a register in the processor/core result or can resultin the transfer of a value in a processor/core register to a DRregister. One predetermined value in the IR register 25 results in alogic “1” being set in the bit-by-pass register 29. Thus, in the exampleof a plurality of TAP units, a string of logic signals entered in allthe IR registers and synchronized by the state machine, can shortcircuit one or more designated TAP units by setting the logic “1” in theby-pass bit register. When the contents of a string of DR registers inthe TAP unit sequence is read out, the designated by-pass bit registersprovide only a logic “1” output, in essence, providing a short circuitfor the test and debug activity for the processor/core associated adesignated tap register.

One of the problems that can arise in the test and debug ofprocessor/cores having advanced power management systems is the changeof power, either by slowing the clock in all of parts of theprocessor/core or by changing the power in all or parts of theprocessor/core. This change in power can result in a processor/core thatcan not be tested by the test and debug unit.

A need has therefore been felt for apparatus and an associated methodhaving the feature of improving test and debug procedures. It is a moreparticular object of the apparatus and associated method to permitselective testing of a number of a plurality of processor. It is yet afurther object of the apparatus and associated method to activate theselected processor/cores using JTAG test and debug procedures. It is astill further feature of the apparatus and associated method to providea technique for determining the status of selected processor/coreparameters for certain processor/cores. It is more particular feature ofthe apparatus and associated method to provide an interface unit betweenthe test and debug apparatus and a plurality of processor/cores that canfacilitate the test and debug procedures. It is a still furtherparticular feature of the apparatus and associated method to provide aninterface unit that includes a TAP unit. It is yet another particularfeature of the apparatus and associated method to provide a statusregisters providing the status of the plurality of processor/cores undertest. It is yet another feature of the apparatus and associated methodto permit the uninterrupted test and debug of a processor/core having anadvanced power management system.

SUMMARY OF THE INVENTION

The aforementioned and other features are provided, according to thepresent invention, by an interface unit between a plurality of TAP unitsof processor/cores on a substrate and a test and debug unit. Theinterface unit includes a TAP unit. The interface unit and theprocessor/cores have a switch unit coupled to each TAP unit. A logicunit in the interface unit, responsive to a signal entered in the TAPunit, provides the control signals for the state machine associated witheach processor/core. A sleep-inhibit signal can be applied to the statemachine preventing the processor/core from entering a lower power state.The interface unit also includes status registers identifying the statusof parameters in each related processor/core. These parameters can betransmitted to the test and debug apparatus through the TAP unit and canidentify whether the processor/core described by the parameters is in astate for testing. If the processor/core is not in a state suitable fortesting, the interface unit, in response to commands from the test anddebug unit, can force the state machine into an appropriate state fortesting the processor/core.

These and other features and advantages of present invention will bemore clearly understood upon reading of the following description andthe accompanying drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram of the apparatus for providing a JTAG interfacebetween an emulation unit and a plurality of processor/core devices.

FIG. 2 is a block diagram of a TAP unit according to the prior art.

FIG. 3 is a block diagram of the apparatus for providing an interfacebetween an emulation unit and a plurality of processor core devices.

FIG. 4 is a block diagram of the switch unit associated with eachprocessor/core and associated with the interface unit according to thepresent invention.

FIG. 5 is a flow chart illustrating how parameters of a processor/coreare forced according to the present invention.

FIG. 6 is flow chart illustrating the technique by which aprocessor/core, after being reincorporated in a test sequence, isresynchronized with the other processor/cores.

DESCRIPTION OF THE PREFERRED EMBODIMENT 1. Detailed Description of theFigures

Referring to FIG. 3, a block diagram of the interface unit 30 mitigatingthe transfer of data between the plurality of processor/cores 11-1N andthe test and debug apparatus is shown. The portion of the currentinvention that differs from FIG. 1 is designated by numbers beginningwith the number three. Coupled to the TAP units 111-11N of eachprocessor/core are switch units 331-33N, respectively. The interfaceunit 30 includes a TAP unit 301. The TAP unit 301 of the interface unit30 is coupled to switch unit 39. The switch units 39 and 331-33N arecoupled in series. The TDI signal from the test and debug unit, i.e.,the emulation unit 2 and the host processing unit 3 of FIG. 1 and FIG.3, is applied to an input terminal of switch unit 39. The outputterminal of switch unit 39 is applied to the input terminal of switchunit 331. The input terminal of each switch unit, except for switch unit39, is coupled to the output terminal of the previous switch unit. Theoutput terminal of switch unit 31N has the TDO signal applied theretoand the TDO signal is returned to the test and debug apparatus.Similarly the TCLK signal from the test and debug apparatus is appliedto a second input terminal of switch unit 39. The TCLK signal is appliedto a second input terminal of switch unit 331 and, consequently, throughthe series-connected switch units 331-33N. From a second output terminalof switch unit 33N, the RTCLK signal is applied to the test and debugunit. The interface unit 30 includes TAP unit 301. Signals from the TAPunit 301 are applied to logic unit 303. The logic unit 303 provides thecontrol signals for all of the switch units 331-33N and 39. In addition,in response to preselected values in the IR register of the TAP unit 30,the values of designated status and control registers 304 will betransferred to a DR register. The status and control registers 304 storeinformation with respect to the power and status for each processorcore. The values in the status registers originate in theprocessor/cores themselves, or originate from the control signals thatset the power, clock, and security parameters in the processor/cores.

The values in the status registers permit the test and debug apparatusto determine when a processor/core is available for testing. Thedetermination of the availability of each processor/core can be donewith the same JTAG procedures as are used in the actual test and debugprocedure.

Each processor/core 11-1N has a power state machine 121-12N,respectively, coupled thereto. The power state machines 121-12N controlthe power level of the coupled processor/core. The power state machinesare coupled to the logic unit 303 in the interface unit.

Through the logic unit 303, the status of the power state machine iscoupled to and entered in the status and control registers 304. Thestatus and control registers 304 store the status of the power appliedto the coupled processor/core. The status of the power applied to eachprocessor core can be communicated to the test and debug unit throughthe interface TAP unit. In this manner, the test and debug unit candetermine whether the power applied to the coupled processor/core isappropriate for test and debug procedures.

The logic unit 303 is coupled to the power state machines 121-12N and tothe status and control register. The state of the power state machine istransmitted to the logic unit 303 and consequently is stored in thelogic unit 304 in response to commands from the test and debug unit canspecify the state of each power state machine.

Referring to FIG. 4, a block diagram of the switch unit 40 associatedwith each processor/core and the interface unit, according to thepresent invention is shown. The TDI signal is applied to a first inputterminal of switch 41. In response to control signals applied toterminal 4 of switch unit 41, the output signal of switch 41 is appliedto the associated TAP unit or to an input terminal 2 of switch 42. Inputterminal 2 of switch 41 is coupled to the associated TAP unit. Thecontrol signals applied to input terminal 4 of switch 42 determineswhether the signal applied to input terminal 1 or the signal applied tothe input terminal 2 of switch is applied to output terminal 3 and isthe TDO signal. The TCLK is applied to the input terminal 1 of switch43. In response to control signals applied to terminal 4 of switch 43,the output signal of switch 43 is applied through terminal 2 to theassociated TAP unit or through terminal 4 to the input terminal 1 ofswitch 44. In response to control signals applied to terminal 4 ofswitch 44, the RTCLK signal applied to terminal 3 is selected for theoutput signal. The presence of the switches permit test and debugprocedures to test one or a selected number of the processor/cores in asingle operation. The disadvantage of the testing of more than oneprocessor/core is that a plurality of signals groups must generated totest the designated processor/cores and a plurality of signal groupsmust be analyzed by the processor. The TMS signal is applied to an inputterminal 1 of switch 45. In response to control signals applied toterminal 4. In response to control signals applied to terminal 4 ofswitch 45, the TMS signal is applied to TAP unit 400. Similarly, switch46 controls the application of the TRST signal to the TAP unit 400.

Referring to FIG. 5, a flow chart for the placing (forcing) aprocessor/core into a selected state, i.e., a state having selectedpower and clock parameters, is shown. In step 51, a test is made of theparameters of the designated processor/core. This test is performed byhaving the logic unit remove the parameters of the designatedprocessor/core that are stored in the register unit. This parameter orthese parameters are applied to the interface TAP unit and transferredto the test and debug unit. In the test and debug unit, a determinationis made if the parameters of the processor/core permit the test anddebug procedures to be performed in step 52. When the answer is yes,then the test and debug procedures continue. When the answer is no instep 52, then the test and debug unit formulates a command, a commandwhich is then applied to the interface TAP unit and then to the logicunit. Based on the received command, the logic unit then applies controlsignals the state machine of the designated processor/core. The statemachine then assumes the state in which the processor/core has theappropriate parameters in step 53. When the state machine confirms tothe logic unit had the designated parameters are present in step 54, theparameters are stored in the register unit 55. Whenever the parametersin the processor/core are changed, this change is reflected in theparameter values stored in the register unit.

Referring to FIG. 6, the technique by which a processor/core, notincluded in the test chain of processor/cores, is resynchronized, i.e.,becomes a member of the test chain is shown. In step 61, the switchassociated with the processor/core in initialized. In step 62, theappropriate (power) state is restored when necessary, e.g., asillustrated in FIG. 5. In step 63, the TRST signal is applied to thestate machine in the TAP unit of a processor/core that was previouslyinactive or was in an inappropriate state. This activity places the TAPunit state machine in the Test Logic Reset state. The TMS signal isapplied to the processor/core TAP unit state machine, thereby placingthe state machine in the Run Test Idle state in step 64. At this pointthe processor/core is now synchronized with the other processor/cores.

Referring next to FIG. 7, a technique for implementing test and debugprocedures in the presence of advanced power management of aprocessor/core is illustrated. In step 71, a sleep-inhibit bit isapplied from the interface logic unit to the state machine. The commandresulting in application of the sleep inhibit bit is generated in thetest and debug unit and applied to the logic unit, the logic unit thentranslating the command to the sleep-inhibit signal applied to theprocessor/core state machine. The sleep-inhibit signal, when applied tothe state machine prevents the state machine from transitioning to alower power state. The sleep-inhibit bit does not affect the activity,even if a lower power is the result, that has already been initiated inthe state machine. Once the sleep-inhibit bit has bee confirmed by thelogic unit in step 72, then step 73 through step 77 is essentially arepeat of FIG. 5. In this procedure, the state of the processor/core inidentified, and, if inappropriate for test and debug procedures, thestate machine is forced into a state suitable for test and debugprocedures. Notice that the sleep-inhibit signal does not prevent thestate machine from being forced into a higher power state, however, oncethat higher power state is achieved, the sleep-inhibit signal preventsthe state machine from reducing the power of the processor/core.

As indicated before with respect to the RTCLK signal, this signal is nota member of the JTAG signal set. However, some processor cores, such asARM units, the TCLK signal is processed by the processor/core and theprocessed signal is referred to as the RTCLK signal. As will be clear,the present invention can work equally well with and without thegeneration of the RTCLK signal.

2. Operation of the Preferred Embodiment

The operation of the present invention can best be understood in thefollowing manner. On a chip having a plurality of processor/cores, eachprocessor core is provided with a TAP unit to provide the interface toJTAG signals. The processor/core TAP units are coupled in series. Aninterface unit is provided that includes a TAP unit. The interface unitTAP unit is coupled in series with the series-coupled TAP units of theprocessor cores. A first set of switches is provided for each TAP unit.In response to control signals, the TDI terminal and the TDO terminalfor a selected TAP unit can be short circuited. Similarly, in responseto second control signals, the TCLK terminal and the RTCLK terminal arecoupled together, i.e. short circuited. The control signals aregenerated in response to TDI signals applied to the interface unit TAPunit by the test and debug unit. In response to the TDI signal, thelogic unit of the interface unit can implement the encoded commands. Inthis manner, the switches can set such that only one TAP unit receivesthe TDI and TCLK signals. The ability to control the state of eachswitch unit permits the selection and therefore the testing of aselected individual processor/core. A plurality of processor/cores canbe selected. In this manner, a plurality of processor/cores can betested simultaneously. The ability of the testing of a plurality ofprocessor/cores requires that test and debug unit generate a string ofdata signals capable in the single access by the test and debugapparatus of placing appropriate bits in the plurality of TAP unit IRregisters of the selected processor/cores. Similarly, when the test anddebug apparatus receive the results of testing the plurality ofprocessor/cores, the test and debug apparatus will have to sort out theresponses from each selected processor/core from a string of data bitsfrom a plurality of DR registers.

The interface unit includes a plurality of status registers. Typicalparameters stored in the status registers relate to power, clock andsecurity conditions. Each of these conditions determines the ability totest the processor/core described by the parameters. When theprocessor/core is not available for test, e.g., the power is off, thisinformation is transmitted through the interface unit TAP unit to thetest and debug unit. The test and debug unit then transmits signalgroups through the interface unit TAP unit to the logic unit appropriatesignals that result in control signals being transmitted to the switchunit associated with the (powered-off) processor/core. The controlsignals then place the switch in a short circuit mode and the TDI andTCLK signals are not applied to the (powered-off) processor/core. Thisprocedure prevents the test and debug procedure from being haltedbecause of a condition in one of the processor/cores.

With respect to the RTCLK signal, this clock signal is a result of apeculiarity of the ARM unit wherein, in order to use the JTAG test anddebug procedures, the TCLK signal must be synchronized with the internalclock of the ARM unit. The resulting (synchronized) signal is referredto as the RTCLK signal and, according to one embodiment of theinvention, when a single ARM unit is in the scan chain, the RTCLK signalfrom the single ARM unit can, depending on the state of the switches,either be applied to each scan chain TAP unit or pass through each scanchain TAP unit. The state of each switch of the scan chain is controlledby the logic unit in the interface unit and, ultimately, by the test anddebug unit. When more than one ARM unit is present, then each of the ARMunits will provide a different RTCLK signal. The net result of thepresence of a plurality of ARM units in the scan chain is to slow theclock rate with the passage of the TCLK or RTCLK signal through the scanchain. When the resulting RTCLK signal is applied to the test and debugunit, the test and debug unit can throttle back the clock rate of theTCLK signal so that the signals in the scan chain can be shifted Iunison.

While the invention has been described with respect to the embodimentsset forth above, the invention is not necessarily limited to theseembodiments. Accordingly, other embodiments, variations, andimprovements not described herein are not necessarily excluded from thescope of the invention, the scope of the invention being defined by thefollowing claims.

1. An integrated circuit apparatus, comprising: a plurality ofprocessor/cores, each said processor core having an input for receivingan associated sleep-inhibit signal, each said processor/core responsiveto the associated sleep-inhibit signal to decrease power consumptiontherein, and said processor/cores including respective in-circuitemulation facilities; an externally accessible input; and an interfaceunit coupled to said processor/cores and said externally accessibleinput, said interface unit configured to provide said sleep-inhibitsignals to the associated processor/cores in response to said externallyaccessible input, said interface unit further configured to permit saidin-circuit emulation facilities to be controlled from said externallyaccessible input.
 2. The apparatus of claim 1, wherein saidprocessor/cores include respective state machines configured to controlpower levels in the respective processor/cores, said state machinescoupled to said interface unit to receive the associated sleep-inhibitsignals.
 3. The apparatus of claim 2, wherein said interface unit isconfigured to permit information indicative of current states of saidstate machines to be accessed from said externally accessible input. 4.The apparatus of claim 3, wherein said interface unit is configured topermit said current states to be changed from said externally accessibleinput.
 5. The apparatus of claim 1, wherein each of said emulationfacilities includes a TAP unit.
 6. The apparatus of claim 5, whereinsaid interface unit includes a TAP unit.
 7. The apparatus of claim 6,including a plurality of switch units respectively coupled to said TAPunits, each of said switch units coupled to another of said switchunits.
 8. The apparatus of claim 7, wherein one of said switch units iscoupled between said externally accessible input and said TAP unit ofsaid interface unit.
 9. The apparatus of claim 7, wherein said switchunits are coupled in a series configuration.
 10. An integrated circuitapparatus, comprising: a plurality of processor/cores, each saidprocessor core having associated therewith a state machine that controlsa power level in said processor/core, and said processor/cores includingrespective in-circuit emulation facilities; an externally accessibleinput; and an interface unit coupled to said state machines and saidexternally accessible input, said interface unit configured to permitinformation indicative of current states of said state machines to beaccessed from said externally accessible input, and said interface unitfurther configured to permit said in-circuit emulation facilities to becontrolled from said externally accessible input.
 11. The apparatus ofclaim 10, wherein said interface unit includes a register for storingsaid information.
 12. The apparatus of claim 11, wherein said interfaceunit includes a TAP unit and logic coupled to said TAP unit and saidregister for accessing said register in response to said TAP unit. 13.The apparatus of claim 12, including a plurality of switch units, eachof said switch units coupled to another of said switch units, one ofsaid switch units coupled between said TAP unit and said externallyaccessible input, a remainder of said switch units coupled torespectively corresponding ones of said emulation facilities.
 14. Theapparatus of claim 13, wherein said switch units are coupled in a seriesconfiguration.
 15. An integrated circuit apparatus, comprising: aplurality of processor/cores, each said processor core having associatedtherewith a state machine that controls a power level in saidprocessor/core, and said processor/cores including respective in-circuitemulation facilities; an externally accessible input; and an interfaceunit coupled to said state machines and said externally accessibleinput, said interface unit configured to permit current states of saidstate machines to be changed from said externally accessible input, andsaid interface unit further configured to permit said in-circuitemulation facilities to be controlled from said externally accessibleinput.
 16. The apparatus of claim 15, wherein said interface unitincludes a register for storing information indicative of said currentstates of said state machines.
 17. The apparatus of claim 16, whereinsaid interface unit includes a TAP unit and logic coupled to said TAPunit and said register for accessing said register in response to saidTAP unit.
 18. The apparatus of claim 17, including a plurality of switchunits, each of said switch units coupled to another of said switchunits, one of said switch units coupled between said TAP unit and saidexternally accessible input, a remainder of said switch units coupled torespectively corresponding ones of said emulation facilities.
 19. Theapparatus of claim 18, wherein said switch units are coupled in a seriesconfiguration.